Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $250.49   13.760%   $284.9574   $284.96   $284.95   $285.00  
  Purchase #2 $147.41   12.626%   $166.022   $166.02   $166.00   $166.00  
  Purchase #3 $221.67   5.640%   $234.1722   $234.17   $234.15   $234.20  
  Purchase #4 $222.26   11.167%   $247.0798   $247.08   $247.10   $247.10  
  Purchase #5 $84.60   10.520%   $93.4999   $93.50   $93.50   $93.50  
  Purchase #6 $82.37   12.356%   $92.5476   $92.55   $92.55   $92.50  
  Purchase #7 $71.42   8.652%   $77.5993   $77.60   $77.60   $77.60  
  7 purchase totals = $1,080.22       $1,195.8782   $1,195.88   $1,195.85   $1,195.90